Firearms, and other projectile devices such as air guns, pellet guns, and bows, are often provided with an aiming device such as, but not limited to a scope, an iron sight, a dot sight, a holographic sight, a shotgun sight, a bead sight, or a ramp sight. In order for the aiming device to have an increased effectiveness, it is important to check and adjust the projectile device and its aiming device such that a point of impact of a projectile launched by the projectile device is aligned with the point of aim of the aiming device. Such alignment, or zeroing of the point of aim and point of impact can make the projectile device far more accurate than a non-aligned or non-zeroed device.
In order to understand existing zeroing processes, it is helpful to look at the trajectory of a projectile fired by a projectile device in comparison to a point of aim for the same projectile device. For convenience, a rifle will be used throughout this specification as an example of a projectile device, but it should be understood that projectile devices include, but are not limited to rifles, pistols, shotguns, firearms, BB guns, pellet guns, air guns, cannons, and bows. FIG. 1 schematically illustrates an example of a person aiming a rifle 30 over a distance of one hundred yards using a scope 32. For convenience, a scope will be used throughout this specification as an example of an aiming device coupled to the projectile device. However, it should be understood that aiming devices include, but are not limited to scopes, iron sights, dot sights, holographic sights, shotgun sights, bead sights, and ramp sights.
The person of FIG. 1 looks through the scope 32 and has a point of aim which may lie along an imaginary sight line 34 which results from an orientation of the scope 32 (for example an up/down or left/right orientation of the scope), an orientation of an optical axis within the scope, and position of the person's eye relative the scope and its optical axis. The sight line 34, along which the point of aim may lie, is a straight line.
A projectile, in this example a bullet, when fired from the rifle 32 will follow a curved path 36 due to the effect of gravity. In the example of FIG. 1, looking at the curves only in the two dimensions of the page, the curved path 36, or trajectory, crosses the line of sight 34 at two points. For this example, those two points are twenty-five yards and two hundred yards. A change in alignment between the optical axis of the scope and the rifle can cause the projectile trajectory to cross the line of sight at different locations or not at all.
Looking only in the two dimensions of FIG. 1, if the desired point of aim was at twenty-five yards or two hundred yards, then the rifle 30 would be zeroed at those distances because the point of aim is aligned with the point of impact at the desired distance. In reality, a projectile device needs to be zeroed in three dimensions. For example, FIG. 2 schematically illustrates a view of a target ring 38 through a scope 32. The point of aim 40 is where the scope's crosshairs 42, 44 meet. An operator has the point of aim directly in the middle of the target ring 38, but FIG. 2 also illustrates an example bullet hole marking a point of impact 46 from when the rifle was fired with the point of aim 40 in the target ring 38. Therefore, zeroing must be performed in three dimensions: for example, up/down, left/right, and out to a particular distance.
Numerous situations may create a need to zero a projectile device, including, but not limited to:                if the projectile device is new;        if the projectile device has a newly installed aiming device;        if the projectile device has been dropped, bumped, or otherwise been roughly handled (the projectile device undergoes traumatic impact);        if the projectile device has been dismantled and put back together;        if the projectile device has been fired numerous times;        if the distance of the desired point of aim changes;        if different projectiles (as one example, different ammunition) will be used with the projectile device; and        if a different operator will be using the projectile device.        
Various solutions have been proposed to help with the zeroing of projectile devices. For example, a recursive solution utilizing multiple rounds (projectiles) is often used when trying to zero projectile devices. As an example of such a recursive solution, a person with a rifle having a scope may aim at a target and then fire. Assuming the rifle starts off aligned to at least shoot the bullet in the vicinity of the point of aim (for example, on a same target area), then the person may measure a horizontal offset 48 and a vertical offset 50 (as illustrated in FIG. 2) between the point of impact 46 and the point of aim 40. Some scopes are equipped with horizontal and vertical adjustment knobs/screws which can then be twisted, dialed, or clicked a particular number of times, per a manufacturer's instructions to compensate for the horizontal offset 48 and vertical offset 50. Unfortunately, it is often difficult to determine how far to turn the adjustment dials because the manufacturers guidelines may be based on a distance different from the desired zeroing distance. Furthermore, the scope adjustment knobs often create audible clicks as they are turned. These clicks need to be counted, but they may be hard to hear in certain environments, especially if hearing protection is being worn (as is often the case around certain firearms). To make matters worse, the springs inside many of the scope adjustment knobs often relax over time, resulting in inaccurate offset compensation even if a desired number of clicks or adjustment turns is used. Given such variability in scope adjustment, a follow-up round, when fired at the target, will most likely not coincide with the point of aim. The process then needs to be repeated, often five to ten times or more. The process is also further complicated and delayed if the scope adjustments are more rudimentary and/or if the projectile device operator is not highly skilled.
Such zeroing techniques can be very wasteful of ammunition or other projectiles. Considering that single rounds of ammunition often cost $1.00 or more each, an enthusiast may be spending $10-20 or more just to zero his weapon each time. According to the National Rifle Association, in 2010 people owned three hundred million firearms in the U.S. alone. Military and law enforcement organizations are also large consumers and users of firearms and other projectile devices which need to be zeroed frequently. The potential reduction in waste and cost savings are staggering if a more efficient method of zeroing projectile devices can be discovered.
Some have proposed methods for zeroing a projectile device which utilize a laser arbor that can be inserted into the barrel of a rifle or other firearm. The laser arbor may be magnetized to temporarily adhere to the inside of the rifle barrel or a properly sized caliber arbor can lodge against the bore while the laser light is shined towards a target as a surrogate for a point of impact since it originated coaxially with the rifle barrel. The scope, or other aiming device, however, cannot be aligned with the laser light since the light travels in a straight line as opposed to the curved trajectory of a bullet. Therefore, if the laser light from such arbor devices is projected onto a target, the scope's point of aim must be aligned somewhere else offset from the laser. This increases the opportunity for human error. Such errors can be complicated by wobble from the magnetically attached laser arbor. Furthermore, some firearms can't be used with a magnetic laser arbor because the barrels are not iron-based and therefore non-magnetic. On top of this, the more serious firearm enthusiasts will not use such a device which intrudes into the barrel crown because it may cause distortion to the barrel's grooving. Still further, such methods require a minimum of two rounds (one initial shot, and at least one follow-up shot to compensate for the flat laser trajectory).
In an attempt to overcome objections to barrel crown intrusion, some manufacturers have created laser cartridges which can be cambered to shine laser light down the inside length of a rifle barrel and out onto a target. While crown insertion is avoided, the linear trajectory of the laser results in similar downfalls to the previously described solution. Furthermore, the spot radius of existing cartridge lasers is quite large, making it further difficult to zero the point of aim onto a point of impact.
Other zeroing solutions provide magnetic grids which can be stuck onto the end of a rifle barrel, rather than inserted into the bore. The scope is then aligned with the grid visible at the end of the barrel. Such methods are useful for “getting a shot on paper” (hitting a paper target), but then usually one of the above methods is needed, typically the recursive method, to truly align the point of aim with the point of impact. Furthermore, as yet another magnetic method, such a technique does not work with firearms made from non-iron-based materials.
Therefore, there is a need for a more efficient, reliable, and money and ammunition saving method and system for aligning a point of aim with a point of impact for a projectile device. Additionally, there is a need for a method and system of indicating a relationship between a point of aim and a point of impact for a projectile device so that a previously zeroed projectile device may be more quickly checked for zero and realigned if necessary in an efficient manner.